Valves which maintain a substantially constant flow rate despite pressure fluctuations at their inlets and/or outlets find widespread use among a spectrum of applications. One notable example is the use of such valves in hydronic system applications wherein water is used as a heat transfer means for heating, cooling and heat transfer. Such systems may have multiple hydronic units, such as heaters, heat exchangers and/or chillers arranged in parallel to receive water from a common feed line. Valves are arranged in series with each unit to control the flow of water to the unit in response to the varying demand of the industrial processes, and heating or cooling functions supported by the system. As a result of the control valves opening and closing to control the flow of water, the feed line may experience significant pressure fluctuations which may lead to undesired variations in the flow rate of water to the various units in the system.
Constant flow rate valves are used to mitigate this problem and help maintain a substantially constant flow rate under fluctuating inlet and/or outlet pressures. However, due to uncertainties inherent in the design of hydronic systems as well as the wide performance variation which may be required of some systems, it is often difficult to specify valves having the necessary characteristics during the system design stage. These uncertainties result in a trial and error approach wherein the adequacy of a valve is often ascertainable only after installation and testing have occurred. Valves must often be replaced because they are not suited to the particular demands of the hydronic system in which they are installed, resulting in increased expense. Furthermore, it is advantageous to have the ability to assert some control over the response sensitivity of constant flow valves to afford a more stable and effective hydronic system.
There is a need for constant flow rate valves which are adjustable in situ to tailor the valve characteristics to the demands of a particular system and avoid the need to swap out valves because of design uncertainties. It is further advantageous to be able to adjust the sensitivity of response of such valves so as to better integrate them into a particular hydronic system.